Noise-free electrical resistor

ABSTRACT

A noise-free electrical device such as a potentiometer which includes a frame having an electrical resistance element mounted thereon. A contact is mounted from the frame for movement relative to the resistance element and an aluminum silicate compound is disposed on the resistance element for reducing the electrical noise between such contact and the resistance element when the contact is moved relative to the resistance element.

[ 1 Oct. 10, 1972 posed g the electrical sistance element when the contact is moved relative to the resistance element.

3,398,004 8/1968 Pendleton et al. Frederick 0 p, Echo Stadlen Ct St t, A l' 2 fee nahelm Ca lf 9 804 Primary Examiner-Lewis H. Myers March 11, 1971 Assistant Examiner-D. A. Tone [21] APPL NOJ 123 230 Attorney-Fulwider, Patton, Rieber, Lee & Utecht [57] ABSTRACT A noise-free electrical device such as a potentiometer Fieid 224 334 which includes a frame having an electrical resistance 5 g element mounted thereon. A contact is mounted from the frame for movement relative to the resistance ele- References Cited ment and an aluminum silicate compound is dis on the resistance element for reducin UNITED STATES PATENTS noise between such contact and the re 4/1967 Kruse........................338/l43 7/1957 Graham.................338/l54X 6/ 1968 Ostrander et al. 17/231 X 5 Claims, 4 Drawing Figures United States Patent Kemp [54] NOISE-FREE ELECTRICAL RESISTOR [72] Inventor:

[22] Filed:

' ALUMINUM SILICATE PATENTEnflcnolmz FIG. 3

FIG. 4

ALUMINUM swans Q Q C INVENTOR.

FIG Feepae/c'k 0. KEMP NOISE-FREE ELECTRICAL RESISTOR BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to electrical devices such as potentiometers which have movable contacts.

2. Description of the Prior Art Many efforts have been made to reduce the noise in electrical devices which have contacts that are movable with respect to resistance elements. Many manufacturing specifications provide that potentiometers must be sufficiently clean to reduce the electrical noise below a selected level. In efforts to' comply with these requirements, it has been proposed that lubricants and the like be interposed between the contact and the resistance element to reduce electrical noise created therebetween. However, there are no devices known to applicant which employ aluminum silicate compounds on the resistance element to reduce electrical noise normally produced when the contacts are moved relative to the resistance element.

SUMMARY OF THE INVENTION The noise-free electrical device of the present invention is characterized by an aluminum silicate compound being disposed between the resistance element and the wiper of a potentiometer to thereby reduce the electrical noise created by relative movement of such contacts.

An object of the present invention is to provide a noise-free electrical device of the type described which is convenient to operate and may be operated without taking undue precaution to maintain the cleanliness thereof.

Another object of the present invention is to provide a noise-free electrical device of the type described which is economical to manufacture.

These and other objects and the advantages of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, partially broken away, of a noise-free electrical device in the form of a potentiometer embodying the present invention;

FIG. 2 is a detail view of a portion of the noise-free 1 electrical device shown in FIG. 1;

FIG. 3 is a graph depicting the voltage change produced by movement of the wiper along the resistance coil of a conventional potentiometer; and

FIG. 4 is a graph depicting the voltage change produced by movement of the wiper along the resistance coil of the potentiometer shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT may be produced by flowing a current through the resistance wire 33 and monitoring the potential between the wiper 15 and one end of the coil 13 and then moving such wiper along the coil to vary the electrical potential. Without the aluminum silicate particles 17 on the coil 13, the voltage does not change along a straight line but, rather, produces voltage spikes created by electrical noise as depicted in FIG. 3. However, with the aluminum silicate compound particles 17 on the resistance coil 13 the variation with wiper movement will be along a generally straight line as shown in FIG. 4 without any electrical noise and the consequent voltage spikes.

The frame 11 is in the form of an electrically insulative body 21 and has an axially extending rotatable drive shaft 25 mounted therein. The resistance coil assembly 13 includes an electrically insulative helical coil spring type structure 31 which is wound with electrical resistance wire 33 that forms the potentiometer resistance. The opposite ends of the resistance wire 33 are connected with electrical terminals 37 and 39.

Carried on the drive shaft 25 in the interior of the housing 21 is an electrically insulative cylinder 45 which is formed on one side with a longitudinal extending channel 47 for receipt of an electrically insulative carriage 51 which mounts an electrically conductive spring blade 53 having a movable contact 55 mounted thereon to form the wiper 15. The carriage 51 is formed with an arcuate groove for receipt of the coils of the helical resistance coil 13 whereby such carriage will be fed along such coil as the shaft 35 is rotated. The contact blade 53 is connected with a brush element (not shown) carried by the carrier 45 and which slidingly engages a brush ring 61 mounted at one end of the housing 11. Connected with the brush ring 61 is an electrical terminal 63 which projects from the housing 1 l.

The aluminum silicate particles 17 are commercially available in dust form having a particle size of less than 60 microns. Consequently, the aluminum silicate composition itself has the consistency of talcum powder and the potentiometer coil assembly 13 may conveniently be dipped therein to provide a light coating of such particles. However, it has been determined that just a few particles of aluminum silicate composition sprinkled on the resistance coil assembly 13 will be sufficient to eliminate electrical noise.

An aluminum silicate composition which has produced a satisfactory result is as follows:

Silica (SiO 74.00% Aluminum Oxide 2 3) 13.69%

Iron Oxide Fe O 2.31% Calcium Oxide (CaO) 0.35% Magnesium Oxide (MgO) l.23% Sodium Oxide (Na O) 1.35% Potassium Oxide (K 0) 6. l 5% Moisture at 105C. 0.07% Combined Water 0.86% Total Water Soluble Salts 0.07% Acid Soluble Matter 0.83% Manganese (Mn) 0.10%

In operation, the potentiometer shown in FIG. 1 may have its terminals 37 and 63 connected in series with an electrical component to which the voltage is to be regulated and the control shaft 25 may be rotated to move the wiper 15 around the interior of the resistance coil assembly 13 to cause such wiper to follow the helical turns of such coil and move the movable electrical contact 55 along the coils of the resistance wire 33 to thereby vary the resistance between the terminals 37 and 63. In observing the voltage variation on an oscilloscope, it has been determined that the voltage on the electrical component to which the voltage is controlled will vary along a relatively straight and unspiked line as shown in FIG. 4. This should be contrasted with the performance of a conventional potentiometer which will produce voltage spikes on an oscilloscope similar to that shown in FIG. 3.

While specific percentages have been set forth in this application defining the elements which may be included in the aluminum silicate composition employed in the noise-free electrical device of present invention, it should be realized that only aluminum and silica are critical to this invention and that the concentrations of both these elements may vary by 20 percent without seriously detracting from the effectiveness in eliminating electrical noise.

While the principle by which the aluminum silicate composition eliminates electrical noise between the contacts during relative movement therebetween is not fully understood, it has been determined that such composition is highly effective in reducing such electrical noise.

From the foregoing it will be apparent that the noisefree electrical device of the present invention provides a convenient means for eliminating electrical noise created by relative movement between movable contacts.

Various modifications and changes may be made with regard to the foregoing detailed description without departing from the spirit of the invention.

I claim: 1. A noise-free electrical device comprising: a frame; a resistance element mounted on said frame; an electrical contact; mounting means for mounting said electrical contact on said frame for movement relative thereto; and an aluminum silicate composition including between 56 and 84 percent Si0 by weight disposed on the resistance element for reducing the electrical noise normally created when said electrical contact is moved relative to said resistance element. 2. A noise-free electrical device as set forth in claim 1 wherein:

said resistance element is in the form of an elongated resistance means; and said mounting means mounts said contact for movement longitudinally along said resistance element whereby the resistance through said contact to one end of said resistance element may be varied by moving said contact longitudinally along said resistance element. 3. A noise-free electrical device as set forth in claim 1 wherein:

said aluminum silicate composition is formed by particles less than 60 microns in size. 4. A noise-free electrical device as set forth in claim 1 wherein:

said aluminum silicate composition includes substantially SiO and l 3.7% A1 0 5. A noise-free e ectrical device as set forth in 01am 1 wherein:

said aluminum silicate composition includes between 1 l and 16.4 percent A1 0 by weight. 

2. A noise-free electrical device as set forth in claim 1 wherein: said resistance element is in the form of an elongated resistance means; and said mounting means mounts said contact for movement longitudinally along said resistance element whereby the resistance through said contact to one end of said resistance element may be varied by moving said contact longitudinally along said resistance element.
 3. A noise-free electrical device as set forth in claim 1 wherein: said aluminum silicate composition is formed by particles less than 60 microns in size.
 4. A noise-free electrical device as set forth in claim 1 wherein: said aluminum silicate composition includes substantially 70% SiO2 and 13.7% Al2O3.
 5. A noise-free electrical device as set forth in claim 1 wherein: said aluminum silicate composition includes between 11 and 16.4 percent Al2O3 by weight. 